Technical Field
The present disclosure relates generally to magnetization manipulation in spintronic devices, and more specifically to techniques for modulating spin orbit spin transfer torque (SO-STT) in spintronic devices.
Background Information
In modern spintronic devices, such as information storage devices (e.g., disks and random access memory), the magnetization directions of ferromagnets (FMs) are utilized to write, store and retrieve information. Effectively manipulating the magnetization direction, e.g. switching the magnetization direction via interactions between spins and charges, is important to the operation of such devices. Traditionally, magnetization manipulation has been achieved via current-induced spin transfer torque (STT) that requires a ferromagnetic spin polarizer in a spin valve or magnetic tunnel junction structure. More recently, techniques have been developed for magnetization manipulation that utilize spin-orbit spin transfer torque (SO-SOT). A typical SO-STT spintronic device (or simply SO-STT device) is structured as a multilayer stack including a ferromagnet (FM) layer adjacent to a metal layer (also referred to as an under or capping layer), among other layers. When a charge current flows through the SO-STT device, a spin current from the adjacent metal layer diffuses into the FM layer and influences the magnetization of the FM. The use of such an arrangement provides various advantages, for example, allowing for low power magnetization manipulation and fast motion of domain walls. In addition, a SO-STT technique allows for separate writing and reading current paths.
While SO-STT is a powerful technique for electrically manipulating magnetization in spintronic devices, there is a need for improved ways of modulating SO-STT. Traditionally, SO-STT devices have required an external magnetic field, referred to as a “symmetry breaking” external magnetic field, be applied to the device to be able to switch magnetization in a deterministic way. If this requirement could be eliminated, it would allow for greater simplification of the device's multilayer stack, which could simplify the fabrication process and/or improve device reliability. Likewise, traditional SO-STT devices have required higher than desired SO-STT switching current density. Improved techniques to enhance and modulate SO-STT magnitude are highly desired for low power spintronic devices (e.g., ultra low power magnetoresistive random-access memory (MRAM) devices) and/or high density magnetic storage devices.